1. Field of the Invention
The present invention relates to an improved injection molding device whereby a thermoset casting resin can be injected into a mold at ambient temperature while substantially eliminating the injection of any gas bubbles into the mold, which would necessarily affect the quality of a finished product. The thermoset casting resin is injected into the mold by a piston having unique characteristics of construction and fiscal properties such that gas bubbles typically formed when one mixes resin with its associated activator are attracted to the sides of the piston body, away from the resin delivery aperture. In addition, the inside distal end of the piston body and the opposed distal end of the ram operatively mounted within the body are uniquely configured to enhance the gas-capturing tendency that results from a static electricity charge generated as the rubber-covered ram distal end moves against the plastic outer body.
2. Description of the Prior Art
The manufacturer of a wide variety of articles and parts by plastic injection molding is, of course, old and well-known. Very broadly stated, when one desires to mold parts from a plastic material and requires that the appearance and accuracy of the final product be of high-quality, rather expensive tool and die metal molds must be prepared for the injection of hot, melted plastic material into the mold. Such a hot injection molding process actually injects melted plastic material into the mold. While extremely high quality articles and parts may be manufactured using hot injection molding, the relative cost of the item being made is substantially determined by the number of items being made due to the expense of the mold and the apparatus necessary to melt the plastic and inject it into the mold. Thus, one encounters significant economic barriers if it is desired to injection mold only a small number of high quality parts.
Of course, articles and parts may also be molded from thermoset casting resins which comprise a mixture of resin and activator, or catalyst. Upon mixing the resin and catalyst in accord with the manufacturer""s instructions, one obtains a flowable thermoset resin that will xe2x80x9chardenxe2x80x9d in a predetermined period of time which is determined by the nature of the resin and its associated activator. However, the chemical reaction which takes place upon mixing the thermoset resin and its activator generates a gas which can become trapped in the thermoset resin as bubbles, and when such material is placed into a mold, the resulting product is frequently unacceptable because of bubbles trapped within the article as it cures, or because of surface blemishes resulting from the presence of bubbles along the surfaces of the mold. Thus, the use of thermoset casting resin for the manufacture of high quality articles and parts, both in terms of physical appearance and strength, has not achieved commercial success. In fact, the practical use of thermoset casting resins today is substantially limited to application by brushing, spraying, or pouring into a mold. None of these procedures and related apparatuses are capable of yielding articles and parts of consistent high quality.
It is therefore clear that a need exists for an injection molding device designed and constructed so that thermoset casting resin can be injected into a mold at ambient temperature such that bubbles of gas do not enter the mold to the detriment of the appearance and physical characteristics of the end product.
The present invention relates to a device for injecting a thermoset casting resin into a mold at ambient temperature while substantially preventing the introduction of gas bubbles into the mold. The device of this invention includes a source of resin, a mold for receiving and curing the resin, a delivery vessel for injecting the resin into the mold, and a conduit in fluid communication between the mold and the delivery vessel. The improvement of this invention comprises the construction of the delivery vessel as a piston having an outer body formed from plastic and a moveable ram operatively disposed for reciprocal movement within the outer body. The outer body has a distal end including an aperture formed therethrough in fluid-communicating relation to the conduit which will deliver the thermoset casting resin to the mold. The moveable ram has a distal end in opposed relation to the body distal end, and the ram distal end defines a convex surface, hereinafter referred to as a ram cone, having its vertex in opposed relation to the body distal end. A surface of the ram cone is preferably formed of rubber, whereby static electricity is generated as the ram cone advances toward the body distal end to deliver the thermoset casting resin into the mold. The static electricity thus generated attracts gas bubbles existing within the resin toward the outer body, away from the delivery aperture. For the purpose of further enhancing the effective capture of gas bubbles along the piston outer body, the distal end of the body also defines a convex surface, hereinafter referred to as a body cone, having its vertex disposed in opposing relation to the ram cone vertex, with the delivery aperture extending through the vertex of the body cone.
By virtue of this construction, as shown in the accompanying drawings and as more fully set forth below, gas bubbles contained within the casting resin are not only attracted to the piston""s outer body, but also tend to remain within the piston inasmuch as casting resin is actually injected into the mold through the aperture formed in the vertex of the ram cone. In effect, a volume of casting resin and xe2x80x9ccapturedxe2x80x9d gas bubbles will remain inside the piston and not be expelled through the delivery aperture because of the opposed convex surfaces defined by the ram cone and the body cone. Virtually all gas bubbles are captured in this volume and not injected into the mold.
The invention accordingly comprises the features of construction, combination of elements, and arrangement of parts which will be exemplified in the constructions hereinafter set forth, and the scope of the invention will be indicated in the claims.